Operating system basics MCQs from the KnowledgeGate question bank
The opening chapters of Operating Systems look easy until an exam turns them into precise questions: what actually counts as multiprogramming, which mode a signal handler runs in, what does and does not interrupt a running process, and what the operating system must save on a context switch. Below are 12 solved MCQs from KnowledgeGate's published question bank, spanning GATE and other recruitment papers, with the exam and year noted on each. Attempt each before reading the answer. Ten of the twelve link to their exact solved page in the introduction to OS and process management modules; the first two are short definitional items whose individual solved pages are not separately indexed, so those point to the introduction module hub instead.
What an operating system is and does
Q1. Which of the following is the primary purpose of an operating system? *(TPSC 2025, see the OS basics module)*
(a) Manage hardware resources
(b) Provide network security
(c) Execute applications
(d) Manage user accounts
Answer: (a) Manage hardware resources.
The operating system's core job is to manage the CPU, memory, storage and devices and to present a clean platform on which applications run. Executing applications and handling accounts are things it enables, but resource management is the defining purpose.
Q2. Which of the following is NOT a system software? *(UGC NET 2020, see the OS basics module)*
(a) Compiler
(b) Operating System
(c) Application Software
(d) Editor
Answer: (c) Application Software.
System software runs and supports the machine itself: the operating system manages hardware, while compilers and editors support program development. Application software is written for user tasks like word processing or browsing, so it sits in the opposite category.
Q3. Which combination of features characterises a multiprogrammed OS? (a) more than one program may be loaded into main memory at once; (b) if a program waits for an event such as I/O, another is scheduled; (c) if a program terminates, another is scheduled. *(GATE 2002, see the solved page)*
(a) a only
(b) a and b
(c) a and c
(d) a, b and c
Answer: (b) a and b.
Multiprogramming means keeping several programs in memory and switching the CPU to another whenever the current one blocks on I/O, so features (a) and (b) together define it. Feature (c), moving on after a program terminates, also happens in plain batch processing, so it does not distinguish multiprogramming.
Q4. Which of the following is an example of a spooled device? *(GATE 1998, see the solved page)*
(a) The terminal used to enter input data for a program
(b) An output device used to print the output of a number of jobs
(c) The secondary memory device in a virtual storage system
(d) The swapping area on a disk used by the swapper
Answer: (b) A printer serving many jobs.
Spooling queues work for a slow device so faster processes need not wait on it, and the printer is the textbook case: jobs pile up in a spool and print in turn. A terminal is interactive, and swap and virtual-storage areas are memory-management mechanisms, not spooling.
System calls and dual mode
Q5. To change the CPU mode from privileged to non-privileged, what is needed? *(GATE 2001, see the solved page)*
(a) A hardware interrupt
(b) A software interrupt
(c) A privileged instruction that does not generate an interrupt
(d) A non-privileged instruction that does not generate an interrupt
Answer: (c) A privileged instruction.
Going the other way, non-privileged to privileged, must be a controlled trap, but here the CPU is already in privileged mode and simply lowers itself. It does that by executing a privileged instruction that clears the mode bit, no interrupt required.
Q6. A processor needs a software interrupt to *(GATE 2001, see the solved page)*
(a) test the interrupt system of the processor
(b) implement co-routines
(c) obtain system services that need execution of privileged instructions
(d) return from a subroutine
Answer: (c) obtain system services.
A software interrupt, or trap, is how a user program crosses into the kernel to request a protected service such as I/O. The CPU switches to privileged mode and jumps to the handler, which is exactly the system-call mechanism.
Q7. A Unix user-level process traps Ctrl-C and runs a signal handler that saves files before terminating. In which mode does the signal handler execute? *(GATE 2005, see the solved page)*
(a) kernel mode
(b) superuser mode
(c) privileged mode
(d) user mode
Answer: (d) user mode.
The kernel does the delivery work in kernel mode, arranging the stack and registers, but the handler itself is user code registered by the process. It therefore runs in user mode, like any other part of the application.
Q8. Match each OS abstraction to what it abstracts: A. Thread, B. Virtual address space, C. File system, D. Signal, against 1. Interrupt, 2. Memory, 3. CPU, 4. Disk. *(GATE 1999, see the solved page)*
(a) A-2, B-4, C-3, D-1
(b) A-1, B-2, C-3, D-4
(c) A-3, B-2, C-4, D-1
(d) A-4, B-1, C-2, D-3
Answer: (c) A-3, B-2, C-4, D-1.
A thread abstracts a CPU's execution stream, a virtual address space abstracts physical memory, a file system abstracts disk storage, and a signal is an interrupt-like notification delivered to a process. Reading each abstraction as "what hardware does this hide" fixes all four pairs at once.
Process states and context switching
Q9. Which of the following does not interrupt a running process? *(GATE 2001, see the solved page)*
(a) A device
(b) Timer
(c) Scheduler process
(d) Power failure
Answer: (c) Scheduler process.
Devices raise hardware interrupts, the timer fires periodic interrupts for time-slicing, and a power failure triggers a critical interrupt. The scheduler is not an external event; it is the kernel code that runs after an interrupt has already occurred, so it does not itself interrupt anything.
Q10. The maximum number of processes that can be in the Ready state on a system with n CPUs is *(GATE 2015, see the solved page)*
(a) n
(b) n squared
(c) 2 to the power n
(d) Independent of n
Answer: (d) Independent of n.
At most n processes can be Running at once, but the Ready queue holds every process that is runnable and simply not yet scheduled. That count is bounded by the total number of processes, not by how many CPUs exist, so it is independent of n.
Q11. Which action is typically NOT performed when switching context from process A to process B? *(GATE 1999, see the solved page)*
(a) Saving A's registers and restoring B's saved registers
(b) Changing address translation tables
(c) Swapping out the memory image of A to disk
(d) Invalidating the translation look-aside buffer
Answer: (c) Swapping out A's memory image.
A context switch saves and restores CPU state, switches the page-table base, and flushes stale TLB entries. Writing A's entire memory image to disk is a separate swapping decision made under memory pressure, not a routine part of every switch.
Q12. Which of the following need not necessarily be saved on a context switch between processes? *(GATE 2000, see the solved page)*
(a) General purpose registers
(b) Translation lookaside buffer (TLB)
(c) Program counter
(d) All of the above
Answer: (b) The TLB.
Registers and the program counter are process state and must be saved to resume correctly. The TLB is a hardware cache of translations that is simply flushed or tagged, not saved and restored, because it can always be rebuilt from the page tables.
Where these 12 fit in your preparation
The set covers the foundation the rest of the syllabus rests on: what an OS is and the multiprogramming and spooling ideas (Q1-Q4), the dual-mode and system-call mechanism (Q5-Q8), and process states and context switching (Q9-Q12). These questions reward precise definitions, so if you missed any, the fix is to state the exact term rather than the general idea, "flushed, not saved" for the TLB, "manages resources" for the OS, and so on.
For the theory behind every answer, work through the introduction to OS module and the process management module, then see how the whole subject fits together in our Operating Systems for GATE breakdown. GATE aspirants get the full sequence inside GATE Guidance by Sanchit Sir; NET aspirants can start from the NET CS category page. Solve, review your misses, and come back a week later.